The photos being of a faucet similar to yours, does not mean that they are like yours. As you can see from the photos, those faucets do have a hex "head" on them. At this point I would suggest you call a plumber. First because you are not sure how to disassemble them, and second, because you might not have the tools or parts to repair them after you get them apart.

: We've got a two-faucet bathtub, about 70+ years old, and a slow drip has turned into a steady leak, so we've been trying to replace the gasket.

: I've removed the faucet handle, brass collar, brass sleeve and porcelin cover, but that's as far as I can go without some advice.

: According to the plumbing supply shop "advisers", I should see a hex-head inside the shaft housing, and backing that off will remove the shaft and gasket assembly. The problem is: ...no hex-head can be seen inside the the shaft housing. Not even a rounded-off one.

: There IS a 1.5" diameter brass tube with female threads that sticks-out an inch or so from the wall, which has a lot of pipe-wrench "bite-marks". This tube surrounds the shaft at the wall. I don't want to try turning this tube, since it may be reverse threaded or something, and breaking it would mean "new plumbing".

: Here's a photo from another web-page, showing old faucets that look somewhat similar to what we have, but I can't see that internal hex-head in the photo.

: http://desktoppub.about.com/library/photos/blplumbing1.htm

: Is it possible that we have a faucet system that doesn't have an internal hex-head?